AJP - Lung Cellular and Molecular Physiology, Vol 262, Issue 2 163-L168, Copyright © 1992 by American Physiological Society
Calcium-dependent regulation of Cl secretion in tracheal epithelium
T. Hartmann, M. Kondo, H. Mochizuki, A. S. Verkman and J. H. Widdicombe
Cystic Fibrosis Research Center, University of California, San Francisco 94143.
In primary cultures of dog tracheal epithelium, isoproterenol produced a
transient increase in short-circuit current (Isc) (duration 30 s; maximal
increase, 32 +/- 5 microA/cm2). This was followed by a more slowly
developing sustained increase (9 +/- 3 microA/cm2), which mimicked the
response to N6, 2'-O-dibutyryladenosine 3',5'-cyclic monophosphate
(DBcAMP). The transient and sustained responses had dissociation constants
for isoproterenol of 2 x 10(-8) and 2 x 10(-9) M, respectively. Bradykinin
(in the presence of indomethacin), substance P, histamine, and thrombin
produced only transient increases in Isc. The time courses of these
transients closely paralleled changes in concentration of intracellular Ca
([Ca2+]i) as measured with fura 2. For different mediators, there was a
significant correlation between the maximal transient increase in Isc and
the maximal increase in [Ca2+]i. The transients in Isc were not associated
with elevation of adenosine 3',5'-cyclic monophosphate (cAMP) and were
unaffected by pretreatment with DBcAMP, which abolishes the steady-state
increase in response to isoproterenol. Both the transient increases in Isc
and [Ca2+]i were inhibited by pretreatment with the Ca chelator
1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid. The phorbol ester
12-O-tetradecanoylphorbol 13-acetate abolished the transient increases in
[Ca2+]i and Isc in response to isoproterenol but not to bradykinin. These
results provide evidence that 1) isoproterenol and bradykinin elevate
[Ca2+]i by different mechanisms, and 2) Ca elevation is associated with a
transient increase in Isc, whereas increased cAMP is associated with a
smaller sustained increase.
